This invention relates to an improvement of a press for powder metallurgy and more particularly to a press or apparatus having simultaneous compression in both directions and comprising die holder which moves with a die at different lower speed than the speed of an upper punch. The upper punch holder and poke rods are simultaneously driven by an upper ram to press and compress simultaneously powder filled in the die from both the upper and lower directions of the die.
In the field of powder metallurgy, it is realized that the powder for metallurgy must be compressed to provide uniform density and subsequently to provide very accurate dimensions for a formed art product. However, in a conventional press, the powder in the die is compressed in different steps respectively by an upper punch and a lower punch, and is further recompressed by the upper punch after compression by the lower punch. Therefore, the uniform density and accurate dimensions of the formed art are not expected.
In the conventional press shown in FIG. 1A, FIG. 1B and FIG. 1C, firstly the powder is filled in a die hole and an upper punch 11 is inserted within the die hole in accordance with driving of an upper ram which is settled at upper portion of press apparatus, then the upper punch starts exerting pressure upon the powder P' as shown in FIG. 1A. In this step, the powder of upper portion in the die hole is compressed as shown by a downward arrow head in FIG. 1A. Secondly, when the upper punch 11 descends further one step, a die 71 which is held by a die holder or die plate descends accordingly with same stroke of the moving distance of the upper punch as shown by a downward arrow head in FIG. 1B, where the powder P' of lower portion in the die hole is simultaneously and upwardly compressed by a fixed lower punch 81 relative to descent of the die 71 and upper punch 11 as shown by an upward arrow head in FIG. 1B, since the lower punch 81 which is positioned in the die 71 is fixed to a fixed lower base. Further, when the die 71 stops descending and is fixed, the upper punch 11 still presses and inserts in the die hole and compresses again the powder downwardly as shown by a downward arrow head in FIG. 1C, then compression of the powder P' is completed.
In FIG. 2 which shows continuous curve lines of one process of the conventional press operation shown in FIG. 1A, FIG. 1B and FIG. 1C, the curve line A shows movement of the upper punch and the other curve line B shows movement of the die. At point a, the upper punch starts pressing the powder and descends in that condition, and from a point b, the die starts descending with the upper punch, and during this movement the lower punch compresses substantially powder upwardly, and then from a portion that the curve line B changes to horizontal line at about 160 or 165 degrees, only the upper punch descends further until 180 degrees, and at a point c the substantial compresion operation is completed. From 180 degrees to 360 degrees of the curve line A, the upper punch ascends for preparation of a next operation, and from 210 degrees to 270 degrees of the other curve line B, the die further descends, and during the lowest portion from 270 degrees to 300 degrees, the formed art product is taken out, and thereafter the die ascends again for preparation of the next operation.
As stated above, in the conventional powder metallurgy press, the powder in the die hole is alternately compressed one by one per one step from respective other directions through three steps, that is, the powder is firstly downwardly compressed, and is secondly upwardly compressed, and is lastly again downwardly compressed, and is subsequently completed. Therefore, the uniform density of the product is not obtained because of reciprocating movement of the powder in the die hole on all such occasions of change of the pressure directions therein, and the accurate dimensions of the product are not expected in consequence of such uneven density and occurrence of defacement of the die, a core or other equipments of the press.